This invention relates generally to flooring tools, and in particular to cushion back cutters. A cushion back cutter is a tool for precisely trimming the edges of carpet seams in preparation for making the seams. As shown in FIG. 1, a prior art cushion back cutter 100 has a body 110; a row separator 115; a row guide 120 that is a straight, thin, beveled surface forming the bottom of the cutter; a blade holding pocket 125 for holding a slotted razor blade 130; and a blade thumbscrew 140. FIG. 2 shows greater detail of one slotted razor blade 130 that is commonly used in the carpet installation trade and in particular with cushion back cutters. Slotted razor blade 130 is generally rectangular in shape, and both long sides have edges 132 that are sharpened along their entire length. Slotted razor blade 130 also includes central slot 134.
As shown in FIG. 1, to install slotted razor blades 130 into the prior art cushion back cutter, blade thumbscrew 140 must first be unscrewed and completely removed. Next, the user inserts the blades in the bottom of blade holding pocket 125 (which has an opening in the bottom of the cutter). Blade thumbscrew 140 can then be re-inserted through a hole in one side of the body, through the central slot 134 in the slotted razor blade 130, and can be tightened into a nut (not shown) welded onto the outside of the opposite side of the body. The slotted razor blade can be extended or retracted from bottom of row guide 120 by loosening the blade thumbscrew 140 and moving the blade inwardly or outwardly from within the blade holding pocket 125.
The angle A of the blade holding pocket 125 holds the slotted razor blade 130 at an angle A of approximately 30° so that a surface B of an edge 132 is exposed to cut the carpet's backing. Surface B is long and cuts with a slicing action. This improves cutting efficiency and blade life, which is important when cutting through coarse carpet backings with thick attached cushions. The distance C between the bottom of the row guide 120 and the bottom corner of slotted razor blade 130 determines the depth of cut. The thicker the carpet's backing, the greater the distance the slotted razor blade 130 must be extended. When the desired depth of cut is established, blade thumbscrew 140 is tightened down, and the cutter is ready to trim seam edges.
Carpet tufts are inserted into carpet backing material in lines. To use cushion back cutter 100, the front of the cutter at row separator 115 is first used as a kind of divider to start a small parted area between two lines of carpet tufts. Once the small parted area is formed, the cutter is pushed forward at handle 180 and row guide 120 maintains the part between the lines of tufts. As shown in FIG. 8, once row guide 115 enters a row between a left line of tufts 201 and a right line of tufts 202, row guide 115 is able to guide the forward motion of the cutter and to position slotted razor blade 130 between the rows of tufts. Thus, as slotted razor blade 130 moves forward with the cutter, the slotted razor blade 130 should cut through the carpet's backing 203, including any attached cushion 204, but should not cut into carpet tufts.
In prior art cushion back cutters, a single slotted razor blade may be inserted into the blade holding slot of the cutter, or a number of them may be inserted. In some prior art cushion back cutters, two or more slotted razor blades are inserted within the same blade holding slot, but only one of them is extended to a cutting position to trim the seam edge (with the others being retracted into blade holding slot). As disclosed in U.S. Pat. No. 3,453,401 to Scott, two slotted razor blades are inserted, but only one is extended to a cutting position, to cut closely to the carpet tufts on the left or right side of a carpet row as desired. When the blade cuts closely to the tufts, a minimum amount of carpet backing will remain at the finished seam, which can reduce unsightly gaps between the tufts. Alternatively, as disclosed in U.S. Pat. No. 3,453,401 to Anderson, the cutter may hold three blades in order to cut left, right, or dead center (as may be required on certain carpets).
Prior art cushion back cutters are economically produced by spot welding stamped sheet metal parts together. As shown in FIG. 3, the prior art cushion back cutter 100 includes a left side plate 150, a center plate 160, and a right side plate 170, all of which are spot welded together to form the body 110 of the cutter. A slot 162 in center plate 160 provides the necessary space to form blade holding pocket 125 in the middle of the cutter that receives slotted razor blades 130. Left side plate 150 and right side plate 170 form the left and right walls of blade holding pocket 125. Center plate 160 includes a bottom bevel 164 forming the row guide 120 of the cutter. Left side plate 150 includes a blade thumbscrew hole 152 and a blade window 154 marked with blade window graduations 156 for setting blade depth. Right side plate 170 includes a nut 172 spot welded onto its outer surface for blade thumbscrew 140.
A problem with the prior art cushion back cutter 100 relates to blade change. Slotted razor blades 130 become dull after trimming long lengths of carpet seam edges, and must be changed repeatedly. Moreover, because the slotted razor blade is sharpened on both edges 132, and because only surface B (FIG. 1) of the blade 130 is being used for actual cutting, the slotted razor blade can be removed from the cutter, rotated, and re-used up to three more times after the first edge becomes dull. But this requires that the user perform the required steps to change or rotate a blade.
As shown in FIG. 3, to change or rotate a slotted razor blade 130, blade thumbscrew 140 must be completely unscrewed and removed from the cutter. This is because blade thumbscrew 140 runs through central slot 134 in slotted razor blades 130. Removing blade thumbscrew 140 is time-consuming and can result in loss of the thumbscrew, which is an expensive part. Furthermore, the maximum depth that the slotted razor blade can cut is limited by the upper end 135 of central slot 134 of slotted razor blade 130 hanging up on blade thumbscrew 140.
It would therefore be desirable to have some other means to hold the blades that did not pass a screw through their central slot, which could improve efficiency of blade change and rotation and might also allow the blade to be extended further to cut thicker carpet backings and attached cushion.
As shown in FIG. 1, another problem with the prior art cushion back cutter 100 relates to the row guide 120 forming the base of the cutter. In prior art cushion back cutters, row guide 120 is formed as a continuous, straight bottom surface on cushion back cutter 100. In some cushion back cutters, the row guide 120 may be beveled to improve its ability to penetrate and follow between the lines of carpet tufts.
However, because row guide 120 is formed as a straight and continuous surface, if a carpet tuft becomes trapped beneath row guide 120, it remains trapped until it is eventually sheared off by a slotted razor blade 130. Due to variations in manufacturing, individual carpet tufts frequently encroach the area between rows of tufts where the cushion back cutter needs to pass. As a result, carpet tufts can be run over and can become trapped by row guide 120 and inadvertently sheared off. If carpet tufts are sheared off by the blade, this will result in gaps in the tufts at the seam. This can produce an unsightly seam, particularly on patterned carpet.
It would therefore be desirable to have some means to prevent carpet tufts from becoming trapped beneath the row guide, which could reduce shearing off of the carpet tufts and thereby produce better looking seams.
The figures depict various embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.